During the Taipei Game Show in Taiwan this weekend, Sony showed a sizzle reel of its PS4 line-up, and included was a possible tease for Metal Gear Rising 2.
You can see it for yourself in the video below pulled from the presentation by AGB, but don't blink. It's only shown for a second. Literally.
If you look at the Metal Gear Rising logo and compare it to the font of the number two shown, it looks pretty damn close if not exact.
In August 2013, a survey linked form the official Metal Gear Solid website asked fans for feedback about Metal Gear Rising: Revengeance and a possible sequel.
While there wasn't any possible information pertaining to what a sequel would entail, it did ask questions regarding whether the survey taker would like to see an earlier or later story, human or cyborg enemies and other questions.
Revengeance was developed by Platinum Games and produced by Kojima Productions for PlayStation 3 and Xbox 360 and was released in February 2013 before heading to PC in January 2014 and on Mac the following September.